1. Field
The present disclosure relates generally to communication, and more specifically to techniques for transmitting pilots in a wireless communication system.
2. Background
In a wireless communication system, a transmitter station (e.g., a base station or a terminal) may utilize multiple (T) transmit antennas for a multiple-input multiple-output (MIMO) transmission to a receiver station equipped with multiple (R) receive antennas. The multiple transmit and receive antennas form a MIMO channel that may be used to increase throughput and/or improve reliability. For example, the transmitter station may transmit up to T data streams simultaneously from the T transmit antennas to improve throughput. Alternatively, the transmitter station may transmit a single data stream from up to T transmit antennas to improve reception by the receiver station.
Good performance may be achieved if the MIMO channel response can be accurately estimated. For example, the receiver station may use the MIMO channel response to perform data detection for the MIMO transmission, to select a spatial mapping matrix to be applied by the transmitter station for the MIMO transmission, etc. Channel estimation is typically supported by transmitting pilot symbols that are known a priori by the receiver station. The receiver station may then estimate the MIMO channel response based on the received pilot symbols and the known pilot symbols.
Channel estimates obtained based on pilot are typically impaired by both noise and interference. The noise may come from various sources such as the wireless channel, receiver electronics, etc. The interference may include inter-antenna interference and inter-transmitter interference. Inter-antenna interference is interference due to transmissions from other transmit antennas. Inter-antenna pilot interference may be present if multiple pilot transmissions are sent simultaneously from all T transmit antennas and the pilot transmission from each antenna interferes with the pilot transmissions from the other antennas. Inter-transmitter interference is interference due to transmissions from other transmitter stations. Inter-transmitter interference may also be referred to as inter-sector interference, inter-cell interference, inter-terminal interference, etc. The inter-antenna interference and inter-transmitter interference may adversely impact channel estimation, which may then degrade data performance.
There is therefore a need in the art for techniques to transmit pilot in a wireless communication system.